The early stages of the utilization of carbohydrates by oral streptococci are being examined biochemically, physiologically and genetically. Such information provides insight not only into the etiology of carious lesions of the teeth, but also into the evolution of oral bacteria. Attention is focused on sucrases, sucrose transport and subsequent inversion and phosphorylation by specific kinases. Extracellular invertases as well as intracellular glucokinase and fructokinase are being purified and characterized from several strains of Stroptococcus mutans. The polysaccharides produced by several isolated glucosyl transferases are being chemically analyzed as well. A number of strains of oral streptococci are being examined for the presence of plasmids. Preliminary results indicate many strains harbor extrachromosomal DNA. The significance of this finding with respect to the pathogenicity and evolution of these species will be examined.